Production of alkali metals



United States Patent 7 PRODUCTION OF ALKALI METALS Richard A. Carpenter, Prairie Village, Kans., assignor to Gallery Chemical Company, Pittsburgh, Pa., :1 corporation of Pennsylvania This invention relates to a new and improved method for the'production of alkali metals and more particularly to a new and improved method for producing alkali metals in substantial yield by reduction of alkali metal hydroxides with iron.

The alkali metals such as sodium, potassium and lithi um are usually prepared by electrolysis of their corresponding chlorides or hydroxides. Another method commonly referred to as the carbothermic reduction process involves heating an alkali metal carbonate and carbon. This latter method results in low yields because oxides of carbon are formed as by-products and a rapid quenching from a temperature in excess of 1000 C. to

beyond either end of the furnace.

2,983,599 Patented May 9, 1961 metal whereas most previous investigators in this art have used excess hydroxide. A 2 to 1 mol ratio of iron to alkali metal was used in most experiments although the reaction is operative from stoichiometric proportions up to the point at which the mol excess of iron mechanically interferes with the vaporization of alkali metal. This process proceeds satisfactorily for sodium and potassium as shown by experimental data. Thermodynamic data show that the process is operative for all of the alkali metals although it should be noted that any thermal reduction process for the preparation of lithium requires extremely high temperatures.

The apparatus used to carry out this process consisted of a reactor made of 1 inch steel pipe 10 inches of which wasencased in a brick furnace while 6 inches extended The furnace was heated by two Globar heaters connected to voltmeter,

was admitted at one end of the reactor tube While vacuum about 500 C. is necessary to prevent a reversal of the reaction. Gay-Lussac and others prepared alkali metals by heating an alkali metal hydroxide with iron. This process always gave poor yields because the hydrogen evolved simultaneously with the alkali metal caused a reversal of the reaction by reducing the ferrous oxide thus forming water which reacted with the alkali metal formed.

It is an object of this invention to provide a new and improved method for producing alkali metals in substantial yields which does not involve electrolysis or carbo thermic reduction. .Another object is to provide an improved reduction process for producing alkali metals from their hydroxides in which the hydrogen and alkali metal are removed in different stages and thus the reversal of the reaction due to hydrogen reduction of ferrous oxide is avoided. Other objects of this invention will become apparent from time to time throughout the specification and claims as hereinafter related. p

This new and improved process will be described more fully in the specification and the novelty thereof will be particularlypointed out and distinctly claimed.

This invention is based upon a ferrothermic process involving two separate steps shown below where M is an alkali metal: Y

In step 1 hydrogen is removed from the alkali metal hydroxide by simple displacement with iron at a relatively low temperature. The resulting mixture of alkali metal oxide, iron oxide, and iron is then heated at a much higher temperature in step 2 to produce more ferrous oxide and vaporize out the sodium. In the actual carrying out of the invention steps 1 and 2 may be carried out with a single charge of reactants which are heated to the different temperatures required for the various stages. In some cases stage 1 may be carried out separately and the mixture of oxides and iron broken up into small sizes before being heated to the temperature required for stage 2. The use of finely divided iron has been found to provide a more intimate mixing and promotes more rapid reaction. It should also be noted that the use of excess iron has been found to favor the production of alkali was applied at the other end of the reactor. At the exit end the pipe was connected to a glass tube which led to the bottom of a 500 ml. suction flask. The outlet of this flask was connected to a hollow stemmed stirrer placed in a two liter Erlenmeyer flask. Thus, the nitrogen swept through the charge and any entrained alkali metal was trapped by impingement on the bottom of the suction flask or by reaction with the water in the Erlenmeyer flask. The bulk of the reduced alkali metal was usually found just beyond the furnace wall and the final steel Temp, C. Percent yield Na 1085 13 1240 38 1320 82 It is apparent from the above data that the yields of sodium increase significantly with increase in temperature and that temperatures of 1300" C. or more are preferred under these operating conditions.

In another series of experiments, metallic potassium was prepared under substantially the same conditions reported above using a 2 to 1 mol ratio of iron to potassium hydroxide. A nitrogen sweep of 0.5 ft./;sec. linear velocity, a reaction time of 5 hours and atmospheric pressure was used but the temperature was varied with the following results:

Temp, C. Percent yield K 900 2 1100 47 1300 82 These data clearly show that metallic potassium can be prepared in good yields using approximately the same conditions as those employed to prepare metallic sodium. V The effect of the linear velocity of nitrogen (velocity measured in the empty reaction tube at the reaction temperature) used on the yield of sodium obtained was also studied in a similar series of experiments using 3 a reaction time of 4 hours and a temperature of 1250" C. at atmospheric pressure with results as follows:

Linear velocity N ft./sec. Percent yield Na The yields of sodium appear to increase significally with increase in velocity of the inert sweep gas. The decrease in yield at the highest sweep velocity reported is believed to be due to a cooling of the charge by the sweep gas. It is believed that if the sweep gas were preheated to the reaction temperature the yield of sodium could be increased further with higher sweep gas velocities.

Another series of experiments were carried out using various pressures with and without a nitrogen sweep. The mol ratio of iron to sodium hydroxide remained constant at 2 to 1. These experiments showed that at approximately 1300 C. substantial yields of metallic sodium could be obtained at atmospheric pressure or pressures as low as 0.1 mm. with or without a nitrogen sweep. However, the best yields were obtained at the lower pressures with a nitrogen sweep. These experiments indicated that the process described is diffusion controlled.

Other experiments have shown that better yields are obtainable when the sintered mixture of oxides and iron obtained from step 1 of this process are pulverized before heating to the reaction temperatures required for steps 2 and 3. Otherwise, at higher temperatures the oxide mass does not permit the sodium formed to vaporize as readily which results in lower yields. The mixed oxide intermediate (from step 1) was therefore prepared as follows: powdered electrolytic iron and flaked sodium hydroxide in a 2 to 1 mol ratio were mixed in a ball mill and placed in a fire clay crucible covered with aluminum foil. The crucible was placed in anelectric furnace and heated slowly to 700 C. for 1 hour. The crucible was cooled and the sintered mass crushed and screened through a 6-12 mesh sieve. These granules of mixed iron, ferrous oxide, and sodium oxide were then heated above 1000 C. with a nitrogen sweep with the following results:

These data clearly show that the best yields of sodium were obtained by heating previously dehydrogenated mixtures of iron and oxides of iron and sodium for 5-6 hours at temperatures 1300 C. or more using low pressures and/or an inert gas sweep.

In adapting this process to continuous operation for making metallic sodium one procedure used is as follows: powdered anhydrous sodium hydroxide and powdered metallic iron in a molar ratio of 1:2. are intimately mixed and heated in a suitable reactor such as a rotary kiln for one hour at 700 C. after which time the hydrogen is completely removed- This dehydrogenated product comprised of a mixture of iron and oxides of iron and sodium is then pulverized and charged to a vertical falling bed retort, and the mixture passed through the externally heated bed countercurrent to a stream of nitrogen gas. The bed temperature is maintained at 1250 C.1300 C. or higher (limited only by the materials ofconstruction used). The sodium liberated is 4 volatilized and leaves the bed with the nitrogen at a temperature of about 1000 C. The nitrogen acts as a sweep gas, diluent and inert atmosphere and materially aids in heat transfer. The sodium is collected by means of a suitable condenser. The charge requires a residence time in the high temperature reaction zone of 1-2 hours or more depending on heat transfer. The spent charge from the sodium reduction step is finally fed into another falling bed reactor where the ferrous oxide is reduced with hydrogen. One half of the required hydrogen is available from the first step of the process and the remainder is supplied from an independent source. Reduction of the ferrous oxide ata temperature of about 600 C. for 2 hours is suflicient to reclaim all. of the iron. The iron and sodium hydroxide remaining are recycled for further processing. Per pass yields of sodium are obtained in this manner.

While several embodiments of this invention have been described it is to be understood that within the scope of the claims appended hereto this invention may be practiced otherwise than as specifically described.

Having thus described this invention and the manner by which it is to be performed, what is desired to be claimed and secured by Letters Patent of the United States is:

l. A method of producing an alkali metal which coinprises heating at a temperature below 1000 C. a mixture.

of iron and alkali metal hydroxide so that the following reaction occurs: 2MOH+2Fe- M o-l- FeO-l-Pe-l-flfi, where M is an alkali'metal, removing substantially all of the hydrogen thus released, heating the mixture to a higher temperature in excess of 1000 C. so that the excess iron in the above reaction reacts to produce additional ferrous oxide and free alkali metal, vaporizing the alkali metal thus formed, and condensing and recovering the alkali metal.

2. A method of producing an alkali metal which comprises heating a mixture of iron and alkali metal hydroxide so that the following reaction occurs:

where M is an alkali metal, removing substantially all of the hydrogen thus released, heating the mixture to a higher temperature so that the excess iron in the above reaction reacts to produce additional ferrous oxide and free alkali metal, vaporizing the alkali metal thus formed, and condensing and recovering the alkali metal, and maintaining the partial pressure of alkali metal vapor over the reaction mixture at a lower'value than the equilibrium pressure for the selected operating temperature by an inert gas sweep of the reactants.

3. A method according to claim 2 in which the second reaction is carried out in a vertical falling bed type reactor.

4. A method according to claim 1 in which the alkali metal is of the class consisting of sodium and potassium.

5. A method according to claim 1 in which the molar ratio of iron to alkali metal hydroxide is in excess of stoichiometric proportions.

6. A method according to claim 2 in which the molar ratio of iron to hydroxide is not less than 2:1.

7.'A method according to claim 2. in which M is sodium.

8. A method according to claim 2 in which M is potassium.

References Cited in the file of this patent UNITED STATES PATENTS France Jan. 13, 1926 

1. A METHOD OF PRODUCING AN ALKALI METAL WHICH COMPRISES HEATING AT A TEMPERATURE BELOW 1000*C. A MIXTURE OF IRON AND ALKALI METAL HYDROXIDE SO THAT THE FOLLOWING REACTION OCCURS: 2MOH+2FE$M2/+FEO+FE+H2$, WHERE M IS AN ALKALI METAL, REMOVING SUBSTANTIALLY ALL OF THE HYDROGEN THUS RELEASED, HEATING THE MIXTURE TO A HIGHER TEMPERATURE IN EXCESS OF 1000*C. SO THAT THE EXCESS IRON IN THE ABOVE REACTION REACTS TO PRODUCE ADDITIONAL FERROUS OXIDE AND FREE ALKALI METAL, VAPORIZING THE ALKALI METAL THUS FORMED, AND CONDENSING AND RECOVERING THE ALKALI METAL. 